The present invention relates generally to filters for use inside blood vessels. More particularly, the present invention relates to thrombus filters which can be securely adjoined at a selected location in the vascular system and selectively removed when the presence of a filter in the vascular system is no longer desired.
There are a number of situations in the practice of medicine when it becomes desirable for a physician to place a filter in the vascular system of a patient. One of the most common applications for vascular filters is the treatment of Deep Venous Thrombosis (DVT). Deep Venous Thrombosis patients experience clotting of blood in the large veins of the lower portions of the body. These patients are constantly at risk of a clot breaking free and traveling via the inferior vena cava to the heart and lungs. This process is known as pulmonary embolization. Pulmonary embolization can frequently be fatal, for example when a large blood clot interferes with the life-sustaining pumping action of the heart. If a blood clot passes through the heart it will be pumped into the lungs and may cause a blockage in the pulmonary arteries. A blockage of this type in the lungs will interfere with the oxygenation of the blood causing shock or death.
Pulmonary embolization may be successfully prevented by the appropriate placement of a thrombus filter in the vascular system of a patient""s body. Placement of the filter may be accomplished by performing a laparotomy with the patient under general anesthesia. However, intravenous insertion is often the preferred method of placing a thrombus filter in a patient""s vascular system.
Intravenous insertion of a thrombus filter is less invasive and it requires only a local anesthetic. In this procedure, the thrombus filter is collapsed within a delivery catheter. The delivery catheter is introduced into the patients vascular system at a point which is convenient to the physician. The delivery catheter is then fed further into the vascular system until it reaches a desirable location for filter placement. The thrombus filter is then released into the blood vessel from the delivery catheter.
In the treatment of Deep Venous Thrombosis, a thrombus filter is placed in the inferior vena cava of a patient. The inferior vena cava is a large vessel which returns blood to the heart from the lower part of the body. The inferior vena cava may be accessed through the patient""s femoral vein.
Thrombus filters may be placed in other locations when treating other conditions. For example, if blood clots are expected to approach the heart and lungs from the upper portion of the body, a thrombus filter may be positioned in the superior vena cava. The superior vena cava is a large vessel which returns blood to the heart from the upper part of the body. The superior vena cava may by accessed through the jugular vein, located in the patient""s neck.
Once placed inside a blood vessel, a thrombus filter acts to catch and hold blood clots. The flow of blood around the captured clots allows the body""s lysing process to dissolve the clots.
The present invention pertains to thrombus filters which may be securely adjoined at a selected location in the vascular system and selectively removed when the presence of a filter in the vasculature systems is no longer required. The present invention also pertains to devices and method for removing a thrombus filter using minimally invasive methods. A thrombus filter in accordance with the present invention includes a first strand formation, a second strand formation and a joined portion. The first strand formation and the second strand formation are both comprised of a plurality of strands, each strand having a joined end and a free end. The joined ends of the strands are joined together proximate the joined portion of the thrombus filter. The strands radiate away from the joined portion of the thrombus filter so that the first strand formation and the second strand formation are both generally conical in shape. The strands of the first strand formation and the strands of the second strand formation radiate in generally opposing directions.
When the thrombus filter is disposed in a blood vessel, at least one of the strand formations acts to trap or capture blood clots. The generally conical shape of the strand formation serves to urge captured blood clots toward the center of the blood flow. The flow of blood around the captured blood clots allows the body""s natural lysing process to dissolve the clots.
The free ends of the strands act as opposing wall contacting members and serve to position the thrombus filter in the center of a blood vessel lumen. In a presently preferred embodiment, the strands are biased to spring outward. The radial force applied to the walls of the blood vessel by the strand formations assists in preventing migration of the thrombus filter within the blood vessel lumen. The generally opposed orientation of the first strand formation relative to the second strand formation also makes migration of the filter less likely. Migration of the thrombus filter within a blood vessel lumen may also be made less likely by the inclusion of an anchor member proximate the free end of each strand.
In a presently preferred embodiment, a sliding member is disposed about the joined portion of the thrombus filter. One or the other of the strand formations may be collapsed by urging the sliding member toward the free ends of the strands. Urging the sliding member toward the free ends of strands collapses the strand formation from a generally conical shape to a generally cylindrical shape. Once the strand formation is collapsed, it may be urged into the lumen of a retrieval catheter.
With one strand formation in the lumen of the retrieval catheter, the entire thrombus filter may be urged into the lumen of the retrieval catheter. Pulling the thrombus filter in the lumen of the retrieval catheter causes the strands of the second strand formation to collapse from a generally conical shape to a generally cylindrical shape. With all strands in a collapsed position, the thrombus filter may be pulled completely into the lumen of the retrieval catheter. With the thrombus filter disposed inside the lumen of the retrieval catheter, removing the thrombus filter from the body of the patient may be accomplished by withdrawing the retrieval catheter from the blood vessel lumen.
In one embodiment of a retrieval catheter, the retrieval catheter includes an outer tubular member, an inner tubular member and a pulling means. One embodiment of the pulling means includes a plurality of retrieval struts each having a distal end. An engaging member is disposed proximate the distal end of each strut. In one embodiment, each engaging member includes a sharp projection. The distal ends of the struts may be selectively urged inward so that the sharp projections penetrate the sliding member of the thrombus filter. Having thus coupled the struts to the sliding member, a pulling force may be applied to the sliding member by pulling on the proximal ends of the struts.
In an additional embodiment of a retrieval catheter, the pulling means may include flanges fixed to the distal end of each strut. The flanges are adapted to be disposed about the fixed portion of the thrombus filter. In a presently preferred embodiment, the joined portion of the thrombus filter has a generally cylindrical outer surface. Also, in a presently preferred embodiment, each flange includes an inner radius which is substantially equal to the outer radius of the joined portion of the thrombus filter. The flanges may be selectively closed around the joined portion of the thrombus filter. When the flanges are closed around the joined portion of the thrombus filter, they butt against each other to form a generally tubular shell around the joined portion of the thrombus filter.
The strands of one or the other of the strand formations may be urged into a collapsed position by urging the flanges toward the free ends of the strands. The flanges may be urged toward the free ends of the strands by pulling on the proximal ends of the struts. Once the strands have been moved into a collapsed position, the strand formation of the thrombus filter may be positioned within the lumen of a retrieval catheter. This may be accomplished percutaneously by pulling on the proximal end of the struts.
With one of the strand formations positioned within the lumen of the retrieval catheter, the remainder of the thrombus filter may also be urged into the lumen of the retrieval catheter. As described previously, the strands of the second strand formation radiate away from the joined portion of the thrombus filter in a generally opposed direction relative to the strands of the first strand formation. The orientation of the strands allows them to be pulled out of the walls of the blood vessel with minimal force. The strands of the second strand formation may be collapsed by simultaneously pushing on the proximal end of the retrieval catheter and pulling on the proximal ends of the struts.
Pulling the thrombus filter into the lumen of the retrieval catheter causes the strands of the second formation to collapse from a generally conical shape to a generally cylindrical shape. With all of the strands in a collapsed position, the thrombus filter may be pulled completely into the lumen of the retrieval catheter. With the thrombus filter disposed inside the lumen of the retrieval catheter, removing the thrombus filter from the body of the patient may be accomplished by withdrawing the retrieval catheter from the blood vessel lumen.